Implantable medical devices (IMDs) detect and treat a variety of medical conditions in patients. Exemplary IMDs include implantable pulse generators (IPGs) or implantable cardioverter-defibrillators (ICDs) that deliver electrical stimuli to tissue of a patient. ICDs typically include, inter alia, a control module, a capacitor, and a battery that are housed in a hermetically sealed container. When therapy is required by a patient, the control module signals the battery to charge the capacitor, which in turn discharges electrical stimuli to tissue of a patient.
The capacitor includes a case, an electrode stack, an inner liner, and an outer liner. The inner and outer liners surround the electrode stack to mechanically immobilize and prevent the electrode stack from contacting the inside of the case. In the case wall or cover is a fill port or tube, which allows introduction of electrolyte into the case. Electrolyte is a medium that facilitates ionic transport and subsequent segregation at the anode and cathode plates of the electrode stack. Ionic segregation at the anode and cathode plates is necessary to store charge on these plates in the capacitor. To ensure generally uniform ionic transport between the plates, the electrolyte is absorbed by the electrode stack. Absorption of the electrolyte occurs through a process that draws the electrolyte into and out of the case via the fill port. Introduction of electrolyte may be repeated to ensure proper wetting of separators and electrodes (electrode stack). During this process, some conventional outer liners may become repositioned in a manner that may partially block the fill port and prevent efficient flow of electrolyte and gas via the fill port. It is therefore desirable to develop an outer case liner that overcomes this limitation.